State of trap set up on river to the north (7)
I believe the answer is:
nigeria
'state' is the definition.
(I know that Nigeria is African country)
'trap set up on river to the north' is the wordplay.
'trap' becomes 'gin' (gin trap is a kind of animal trap).
'set up' says the letters should be written backwards (in a down clue, letters go up).
'on river' becomes 'aire' (I can't explain this - if you can you should give a lot more credence to this answer).
'to the north' says the letters should be written in reverse (in a down clue, letters go up or 'northward').
'gin' written backwards gives 'nig'.
'aire' written backwards gives 'eria'.
'nig'+'eria'='NIGERIA'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for nigeria that I've seen before include "part of Africa" , "African country r" , "West African republic" , "West African state" , "African country, capital Abuja" .)